Joe Touch wrote:
9. ICMP
ICMP does not carry any port information and is consequently
problematic for address sharing mechanisms.
ICMP messages are specifically intended to include enough of the
transport header to enable port demuxing at the end receiver.
I think it says ICMP information messages such as echo request
do not have port numbers.
However, ID and sequence number field of echo request can be
used (overridden) as source and destination port numbers,
respectively.
As the fields are copied as is from echo request to echo reply,
ID and sequence number field of echo request must be
used as destination and source (reversed) port numbers,
respectively.
It's implemented for end to end NAT and is working with "ping"
and "traceroute".
11. Fragmentation
When a packet is fragmented, transport-layer port information (either
UDP or TCP) is only present in the first fragment. Subsequent
fragments will not carry the port information and so will require
special handling.
?INT? The ID will be incorrect too; it may not be unique as required
when viewed from the outside.
Port based redirection MUST be done after fragmentation reassembly.
That's all and is no special.
Masataka Ohta
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